1. Field of the Invention
The present invention relates to a method for reducing image noise. More particularly, the present invention relates to a method for reducing scanned image noise and reducing scanned image file capacity.
2. Description of the Related Art
A scanner is a machine having a function similar to a camera combined with a Xerox machine, as the scanner can copy an image to a file and then print it out on a printer. In the early days when the scanner was first produced, the price was expensive and only a few people or offices could afford one. Recently, because the manufacturing techniques of optical scan heads are mature and mass production of scanners is now available, the price of scanners has gone down and the scanner has become the next must-have peripheral for mainstream PC users. The scanner market is heating up rapidly.
The scanner can be classified into several types including the handy scanner, sheetfed scanner, business card scanner, film scanner, drum scanner and flatbed scanner, according to the prices and functions thereof. A flatbed scanner is an opto-electric device capable of converting the printed data on a document into digital form for processing by the computer. The document that is to be scanned is fixedly placed on a transparent glass plate on the flatbed scanner and a movable scan head moves over the document to make a scan that converts the printed data on the document into digital form. The scan head is optically coupled to a linear array of light-sensing cells such as a charge-coupled device (“CCD”), each cell corresponding to a pixel in the scanned image. Because a flatbed scanner has a simple structure and is easy to use, it has become mainstream among the varieties of scanners.
When a scanner is used for scanning a document, image noise of the scanned image of the document is produced due to the scanner devices. The image noise may reduce the image quality of the scanned image and make variations compared with the document. A conventional method for reducing image noise is to decrease the color level of the scanned image by a hardware filter, for example, an optical filter. Since the color level of each pixel of the scanned image is averaged in order to average and minimize the image noise, the scanned image quality may be blurred by this method. Another conventional method for reducing image noise is to decrease the color level of the scanned image by a software filter, for example, to set a color scale level as the noise level of a scanned image. But after the color level of every pixel of the scanned image is subtracted by the noise level in order to minimize the image noise, the scanned image quality may also be reduced.